X-ray laser based on OFI is a promising way to realize the table-top X-ray laser.A simple model to describe the electron energy distribution in plasma produced by circularly polarized optical-field-induced ionization is constructed on the basis of ADK tunneling ionization theory.The ionization rate,threshold intensity,residual energy and electron energy distribution of Pd-like Xe system based on optical-field-induced ionization are calculated.The results are useful to further experments on X-ray laser of Pa-like Xe system.
This paper proposes a novel one-colour Xe-Kr laser induced collisional ionization system. Considering the level scheme of the system, it finds that the initial state of the reaction—the four 4f levels with even J of Xe—can be prepared through method of four-photon resonant excitation by dye laser with wavelength of ～440 nm. Absorption of an additional photon (the transfer laser) of the same wavelength will complete the laser induced collisional ionization process. The resonance enhanced ionization spectrum of Xe by four laser photons at ～440 nm is measured through time-of-flight mass spectrometry, this aims at the preparation of the initial state of the system proposed. The Stark broadening of the measured spectrum is observed and consistent with the previous study. Analysis of the measured resonance ionization spectrum implies the feasibility of ～440 nm four-photon resonant excitation of the initial 4f state of the Xe-Kr system proposed in this paper, which prepares for a further experiment of laser induced collisional ionization.
The four-level model of laser-induced collisional energy transfer(LICET) for the ion-ion collision system is established based on the time-dependent Schro¨dinger equation for the electron dynamics,through which the equations of motion of the probability amplitudes and cross section of the collision system are obtained.Numerical calculations are performed for the Ca+-Sr+ system,with the results showing that the peak of the LICET spectrum appears at a resonant frequency of the transfer laser.The magnitude of the obtained collision cross section is in the order of 10 16 cm2,and is comparable to that obtained in atomic systems,which indicates the validity of the established four-level model.
We present a valence orbital method of calculating high-order harmonic generation from a diatomic molecule with arbitrary orientation by using a space rotation operator. We evaluate the effects of each valence orbital on harmonic emissions from N2 and O2 molecules in detail separately. The calculation results confirm the different properties of harmonic yields from N2 and O2 molecules which are well consistent with available experimental data. We observe that due to the orientation dependence of σ and π orbitals, the bonding orbital (σ2pz)2 of N2 determines the maximum of harmonic emission when the molecular axis of N2 is aligned parallel to the laser vector, and the magnitude of the high harmonic signal gradually weakens with the orientation angle of molecular axis increasing. But for O2 molecule the antibonding orbitals (π 2py )1 and (π 2pz )1 contribute to the maximum of harmonic yield when O2 is aligned at 45 and bonding orbitals (π2py)2 and (π2pz)2 slightly influence the orientation angle of maximum of harmonic radiation not exactly at 45 .
